Asymmetrical frontal brain activity holds promise as a marker of risk for depression. Over 40 studies suggest that resting frontal electroencephalographic (EEG) asymmetry may serve as an indicator of a trait-like diathesis to respond to emotional situations with a pattern of emotional negativity and behavioral withdrawal. Moreover, resting frontal EEG asymmetry distinguishes depressed individuals -- those currently symptomatic as well those as in remission -- from never-depressed individuals. These findings suggest that frontal EEG asymmetry is more than a correlate of a depressive episode, potentially serving as a liability marker for the development of depression. Such a marker could have prognostic and etiological value, but superimposed on the trait-like stability are fluctuations that vary as a function of occasion of assessment or experimentally manipulated emotion. Estimates of the stability of frontal EEG asymmetry are in the range of.60, suggesting that trait factors are substantial, but that variation across assessments may limit the utility of asymmetrical frontal brain activity as a trait-like risk indicator for depression. Such factors may underlie the few inconsistent findings in this literature. The present proposal represents a necessary step in the programmatic investigation of frontal EEG asymmetry as a potential risk indicator for depression, by evaluating three distinct sources of variability in frontal EEG asymmetry: 1) Stable trait consistency across multiple assessments; 2) Occasion-specific fluctuations from one assessment to the next; and, 3) State-dependent changes within a single assessment. During four visits, trait resting as well as state manipulated frontal EEG asymmetry will be assessed in depressed and nondepressed subjects. This design will allow us to address several specific aims, including: 1) To assess the relative contributions of trait, occasion, and state variance in frontal EEG asymmetry; 2) To assess whether frontal EEG asymmetry has characteristics that suggest it may profitably serve as a marker of risk for major depressive disorder; and, 3) To assess the acute impact of a widely used selective serotonin reuptake inhibitor on frontal EEG asymmetry, as medication effects have been largely unexplored. Secondary aims address methodological and treatment-related questions, as well as assessing gender and menstrual cycle effects that may moderate the relationship between frontal EEG asymmetry and depression.